1. Technical Field
This invention pertains to processes for producing reaction product through equilibrium-limited reactions, such as esterification and alcoholysis (or transesterification) reactions. The invention is particularly useful in esterification processes such as to make carboxylic acid esters, e.g., butyl acrylate and ethylhexyl acrylate.
2. Background of the Invention
Equilibrium-limited reactions generally involve the reaction of two or more reactants to produce at least one product and, typically, a co-product. In order to achieve a greater conversion to the desired product(s), various techniques have been suggested such as removing the co-product and/or product from the reaction menstruum to maintain a driving force toward the product.
Equilibrium-limited reactions can be conducted in a single reactor with product being selectively removed from the reaction menstruum or in a plurality of reactors in which product is separated from the reaction menstruum in each of the reactor stages. One type of single reactor process is disclosed in U.S. Pat. No. 3,700,726 which discloses a process for making glycol ether acetates in which a reactor operates at a temperature of about 150xc2x0 C. to 225xc2x0 C. and a pressure of about 25 psia to about 150 psia to effect the reaction of a lower alkyl acetate with a glycol ether in the presence of catalyst selected from aluminum alkoxides, titanium alkoxides and dialkyl tin oxides. A vapor is withdrawn from the reactor and is distilled to recover the co-product alcohol and a bottoms fraction which is recycled to the reactor. A liquid is withdrawn from the reactor and is flashed in a flash column operating at about 130xc2x0 C. to 180xc2x0 C. The overhead from the flash column contains the product ester which is subjected to distillation for purification and the bottoms from the flash column, which contains catalyst, is recycled to the reactor.
Another type of single reactor process is disclosed in U.S. Pat. No. 4,280,010 which discloses a continuous process for making alkyl acrylates free from ether by reacting acrylic acid with a C1 to C4 alkanol in a molar ratio of 1:1 to 1:2 in the liquid phase. The process is conducted at a temperature of 80xc2x0 C. to 130xc2x0 C. and a pressure of 100 to 760 mm Hg in the presence of a sulfuric acid or organic sulfonic acid catalyst, and the resulting alkyl acrylate is distillatively purified. As part of the distillation, an azeotropic mixture of alkyl acrylate, reaction water and unreacted alkanol is distilled off near the head of a first distillation zone which is mounted on the reaction zone.
Yet another type of single reactor process is disclosed in European Patent No. 0 733 617 which discloses a process for the continuous esterification of an alkanol with (meth)acrylic acid in the presence of proton-donating catalysts in a homogeneous, liquid, solvent-free phase in which the water generated in the reaction and the produced alkyl esters are continuously separated as an aqueous azeotrope via the head of a rectification zone mounted on the reaction zone and which has a head pressure of 0.1-1 atmospheres, to give a pure (meth)acrylate.
European Patent Application No. 0 779 268 discloses a method for recovering n-butyl acrylate substantially free of acrylic acid from an esterification reaction mixture by distilling from an esterification reactor a vaporized mixture of acrylic acid, n-butyl acrylate, n-butanol and water, and condensing the vaporized mixture to provide a first condensate of an organic phase and an aqueous phase. A portion of the organic phase and aqueous phase is then fed to an acrylic acid separation column. An azeotropic mixture of n-butanol, n-butyl acrylate and water is distilled from the acrylic acid separation column at an aqueous reflux ratio of 8.5:1 to 17:1, and an acrylic acid bottom stream is removed from the distillation column and recycled to the esterification reactor. Refluxing any portion of the organic phase is detrimental to the operation of the acrylic acid separation column (see page 13, line 58 through page 14, line 5). The overhead mixture is condensed to provide a second condensate which is separated into a n-butyl acrylate rich organic phase and an aqueous phase. The n-butyl acrylate rich organic phase is then removed substantially free of acrylic acid. Additional reactants are recovered and recycled after treatment in a separate hydrolytic recovery unit and a cracking reactor.
Frequently, where the reaction is conducted in a single reactor, the residence time to secure the desired conversion results in a large reactor volume per unit volume of product. Moreover, substantial amounts of vapor are typically generated to remove product and co-product, and vaporized reactants are recovered and returned to the reactor, resulting in significant energy costs. Reactant recovery itself may pose difficult problems or require elaborate separation schemes. In some instances, to vaporize the product for its removal, temperatures may be required that result in undesired side reactions and/or subatmospheric pressures are employed that further increase operating costs.
Accordingly, processes for conducting equilibrium-limited reactions are sought that reduce total reactor volumes and number of reactors, minimize reactant recovery problems, and provide sought conversions to the product without the need to resort to significant energy use, e.g., unduly high temperatures or excessive vacuums, in conducting the reactions.
The processes of this invention relate to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product in a single reaction zone, wherein the reaction zone temperature and pressure are sufficient to crack heavies, e.g., Michael-Addition heavies, formed in or introduced into said single reaction zone and to vaporize at least a portion of the ester product upon production thereof. An acid separation column containing a rectification zone and a stripping zone provides (in the rectification zone) an overhead fraction comprising the at least one ester product and (in the stripping zone) a bottoms fraction comprising water and the at least one carboxylic acid, in which at least a portion of the bottoms fraction is supplied by controlled means to the single reaction zone sufficient to provide stable and efficient operation of the acid separation column and single reaction zone. While typically only one ester product is ultimately sought, the processes of this invention may make possible the simultaneous formation of two or more ester products. For instance, acrylic acid may be reacted with a mixture of ethanol and butanol to produce the corresponding ethyl and butyl acrylates.
The processes of this invention relate in part to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product comprising:
a. reacting at least one carboxylic acid-containing feedstock with at least one alcohol-containing feedstock in the presence of an esterification catalyst in a single reaction zone maintained under reaction conditions sufficient to produce at least one ester product, said reaction conditions comprising a temperature and pressure sufficient to crack heavies formed in or introduced into said single reaction zone and to vaporize at least a portion of said at least one ester product upon production thereof;
b. withdrawing vapor from said single reaction zone, and introducing said withdrawn vapor into the lower portion of an acid separation column, said acid separation column comprising a rectification zone above the point where said withdrawn vapor is introduced into said acid separation column and a stripping zone below the point where said withdrawn vapor is introduced into said acid separation column, to provide (in said rectification zone) an overhead fraction comprising said at least one ester product and (in said stripping zone) a bottoms fraction comprising water and said at least one carboxylic acid;
c. withdrawing from the acid separation column the bottoms fraction and supplying at least a portion of the withdrawn bottoms fraction to said single reaction zone by controlled means sufficient to provide stable and efficient operation of said acid separation column and said single reaction zone; and
d. withdrawing from the acid separation column the overhead fraction and recovering said at least one ester product from the overhead fraction.
In this embodiment, lower purity feed streams, for example, crude butanol streams containing dibutyl ether or crude acrylic acid streams containing high concentrations of acrylic acid dimer or other Michael-Addition heavies may be utilized in the processes of this invention as well as heavy residue-containing streams generated from other processes which employ similar equilibrium-limited reactions, e.g., integrated equilibrium-limited processes. Also, in this embodiment, the rate of supply of withdrawn bottoms fraction from the acid separation column to the single reaction zone can be controlled and adjusted according to the needed water rate for formation of the product/water azeotrope, e.g., butyl acrylate/water azeotrope. If the rate is too low, the liquid level in the single reaction zone will rise due to buildup of product, e.g., butyl acrylate, concentration leading to inefficient operation of the single reaction zone. If the rate is too high, the excess water will remove byproduct, e.g., butoxy propionate (BBP), from the single reaction zone by a BBP/water azeotrope, which results in a higher BBP concentration in the acid separation column leading to unstable and inefficient operation of the acid separation column.
The processes of this invention also relate in part to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product comprising:
a. reacting at least one carboxylic acid-containing feedstock with at least one alcohol-containing feedstock in the presence of an esterification catalyst in a single reaction zone maintained under reaction conditions sufficient to produce at least one ester product, said reaction conditions comprising a temperature and pressure sufficient to crack heavies formed in or introduced into said single reaction zone and to vaporize at least a portion of said at least one ester product upon production thereof;
b. withdrawing vapor from said single reaction zone, and introducing said withdrawn vapor into the lower portion of an acid separation column, said acid separation column comprising a rectification zone above the point where said withdrawn vapor is introduced into said acid separation column and a stripping zone below the point where said withdrawn vapor is introduced into said acid separation column, to provide (in said rectification zone) an overhead fraction comprising said at least one ester product and (in said stripping zone) a bottoms fraction comprising water and said at least one carboxylic acid;
c. introducing at least one alcohol, which may be the same or different as the alcohol contained in said alcohol-containing feedstock, into said acid separation column in the region between the bottom of the acid separation column and the point where said withdrawn vapor is introduced into the acid separation column, in an amount sufficient to provide stable and efficient operation of said acid separation column, e.g., minimize or eliminate foaming in said acid separation column;
d. withdrawing from the acid separation column the bottoms fraction and supplying at least a portion of the withdrawn bottoms fraction to said single reaction zone by controlled means sufficient to provide stable and efficient operation of said acid separation column and said single reaction zone; and
e. withdrawing from the acid separation column the overhead fraction and recovering said at least one ester product from the overhead fraction.
In this embodiment, operational stability is imparted to the acid separation column through introduction of the alcohol, either fresh or recycled, into the acid separation column in the region between the bottom of the acid separation column and the point where the withdrawn vapor from the single reaction zone is introduced into the acid separation column. It is important to control foaming in the distillation column base not only for operational stability and efficiency but also for minimizing carboxylic acid breakthrough in the overhead make. Foaming may result from unstable composition regions and/or a high base circulation rate in the acid separation column.
The processes of this invention further relate in part to conducting an equilibrium-limited reaction of at least one unsaturated carboxylic acid and at least one alcohol to produce at least one unsaturated ester product comprising:
a. reacting at least one unsaturated carboxylic acid-containing feedstock with at least one alcohol-containing feedstock in the presence of an esterification catalyst in a single reaction zone maintained under reaction conditions sufficient to produce at least one unsaturated ester product, said reaction conditions comprising a temperature and pressure sufficient to crack heavies formed in or introduced into said single reaction zone and to vaporize at least a portion of said at least one unsaturated ester product upon production thereof;
b. withdrawing vapor from said single reaction zone, and introducing said withdrawn vapor into the lower portion of an acid separation column, said acid separation column comprising a rectification zone above the point where said withdrawn vapor is introduced into said acid separation column and a stripping zone below the point where said withdrawn vapor is introduced into said acid separation column, to provide (in said rectification zone) an overhead fraction comprising said at least one unsaturated ester product, lower boiling byproducts, higher boiling byproducts and said at least one alcohol, and (in said stripping zone) a bottoms fraction comprising water and said at least one unsaturated carboxylic acid, and introducing at least one polymerization inhibitor into said acid separation column;
c. withdrawing from the acid separation column the bottoms fraction and supplying at least a portion of the withdrawn bottoms fraction to said single reaction zone by controlled means sufficient to provide stable and efficient operation of said acid separation column and said single reaction zone;
d. withdrawing from the acid separation column the overhead fraction and introducing at least a portion of the withdrawn overhead fraction into at least one splitter distillation column to provide an overhead fraction comprising said lower boiling byproducts and said at least one alcohol and a bottoms fraction comprising said at least one unsaturated ester product and said higher boiling byproducts, and introducing at least one polymerization inhibitor into said at least one splitter distillation column;
e. withdrawing from the at least one splitter distillation column the overhead fraction and introducing the withdrawn overhead fraction into at least one alcohol recovery distillation column to provide an overhead fraction comprising said lower boiling byproducts and a bottoms fraction comprising said at least one alcohol, and introducing at least one polymerization inhibitor into said at least one alcohol recovery distillation column;
f. withdrawing from the at least one alcohol recovery distillation column the bottoms fraction (and recycling at least a portion of said bottoms fraction) and the overhead fraction (and purging at least a portion of said overhead fraction);
g. withdrawing from the at least one splitter distillation column the bottoms fraction and introducing the withdrawn bottoms fraction into at least one ester distillation column to provide an overhead fraction comprising said at least one unsaturated ester product and a bottoms fraction comprising said higher boiling byproducts and at least one polymerization inhibitor, and introducing at least one polymerization inhibitor into said at least one ester distillation column and/or said withdrawn bottoms fraction from the at least one splitter distillation column prior to introducing said withdrawn bottoms fraction into said at least one ester distillation column;
h. withdrawing from the at least one ester distillation column the bottoms fraction comprising at least one polymerization inhibitor and supplying at least a portion of the withdrawn bottoms fraction to the acid separation column, the at least one splitter distillation column and/or the at least one alcohol recovery distillation column, in an amount sufficient to minimize or eliminate polymerization of said unsaturated carboxylic acid and/or said unsaturated ester product; and
i. withdrawing from the at least one ester distillation column the overhead fraction comprising said at least one unsaturated ester product.
In this embodiment, polymerization inhibitors are reused in the process by recycling the withdrawn bottoms fraction containing polymerization inhibitor from the at least one ester distillation column to the acid separation column, the at least one splitter distillation column and/or the at least one alcohol recovery distillation column. In addition to being cost effective, the recycling of polymerization inhibitors to the various distillation columns controls undesirable polymerization, for example, reactive monomers such as acrylic acid and butyl acrylate readily form polymer via free radical polymerization if not well inhibited. This process is further cost effective in that the recycle stream returns heavies for cracking to the reactor.
The processes of this invention yet further relate in part to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product comprising:
a. reacting at least one carboxylic acid-containing feedstock with at least one alcohol-containing feedstock in the presence of an esterification catalyst in a single reaction zone maintained under reaction conditions sufficient to produce at least one ester product, said reaction conditions comprising a temperature and pressure sufficient to crack heavies formed in or introduced into said single reaction zone and to vaporize at least a portion of said at least one ester product upon production thereof;
b. withdrawing vapor from said single reaction zone, and introducing said withdrawn vapor into the lower portion of an acid separation column, said acid separation column comprising a rectification zone above the point where said withdrawn vapor is introduced into said acid separation column and a stripping zone below the point where said withdrawn vapor is introduced into said acid separation column, to provide (in said rectification zone) an overhead fraction comprising said at least one ester product, lower boiling byproducts, higher boiling byproducts and said at least one alcohol, and (in said stripping zone) a bottoms fraction comprising water and said at least one carboxylic acid;
c. withdrawing from the acid separation column the bottoms fraction and supplying at least a portion of the withdrawn bottoms fraction to said single reaction zone by controlled means sufficient to provide stable and efficient operation of said acid separation column and said single reaction zone;
d. withdrawing from the acid separation column the overhead fraction and introducing at least a portion of the withdrawn overhead fraction into at least one splitter distillation column to provide an overhead fraction comprising said lower boiling byproducts and said at least one alcohol and a bottoms fraction comprising said at least one ester product and said higher boiling byproducts;
e. withdrawing from the at least one splitter distillation column the bottoms fraction and introducing the withdrawn bottoms fraction into at least one ester distillation column to provide an overhead fraction comprising said at least one ester product and a bottoms fraction comprising said higher boiling byproducts;
f. withdrawing from the at least one ester distillation column the bottoms fraction (and recycling at least a portion of said bottoms fraction) and the overhead fraction (comprising at least said one ester product);
g. withdrawing from the at least one splitter distillation column the overhead fraction and introducing the withdrawn overhead fraction into at least one alcohol recovery distillation column to provide an overhead fraction comprising said lower boiling byproducts and a bottoms fraction comprising said at least one alcohol;
h. withdrawing from the at least one alcohol recovery distillation column the bottoms fraction and supplying at least a portion of the withdrawn bottoms fraction to said acid separation column in the region between the bottom of the acid separation column and the point where said withdrawn vapor is introduced into the acid separation column, in an amount sufficient to provide stable and efficient operation of said acid separation column, e.g., minimize or eliminate foaming in said acid separation column, and/or said single reaction zone; and
i. withdrawing from the at least one alcohol recovery distillation column the overhead fraction (and purging at least a portion of the withdrawn overhead fraction).
In this embodiment, unreacted alcohol is reused in the process by recycling the withdrawn bottoms fraction containing unreacted alcohol from the at least one alcohol recovery distillation column to the acid separation column in the region between the bottom of the acid separation column and the point where the withdrawn vapor from the single reaction zone is introduced into the acid separation column and/or said single reaction zone. In addition to being cost effective, the recycling of unreacted alcohol to the acid separation column helps to impart operational stability to the acid separation column as described above.
In another embodiment, the above processes also comprise introducing at least a portion of (i) the withdrawn overhead fraction from the acid separation column, (ii) the withdrawn overhead fraction from the at least one splitter distillation column, and/or (iii) the withdrawn overhead fraction from the at least one alcohol recovery distillation column, to a water distillation column to provide an overhead fraction comprising said at least one alcohol and a bottoms fraction comprising water, withdrawing from the water distillation column the bottoms fraction (and purging at least a portion of the bottoms fraction), and withdrawing from the water distillation column the overhead fraction and supplying at least a portion of the overhead fraction to said acid separation column in the region between the bottom of the acid separation column and the point where said withdrawn vapor from the single reaction zone is introduced into the acid separation column and/or said single reaction zone. In this embodiment, unreacted alcohol is reused in the process by recycling as described above.
In yet another embodiment, this invention relates to a batchwise or continuously generated mixture comprising at least 50.0 weight percent butyl acrylate and containing not more than 8 parts per million acrylic acid. Such mixtures result from the practice of this invention when carboxylic acid, e.g., acrylic acid, breakthrough in the overhead make from the acid separation column is minimized or eliminated. The unique configuration of the single reaction zone and acid separation column is advantageous in enabling the production of an overhead make (from the acid separation column) having high concentrations of butyl acrylate, e.g., at least 50.0 weight percent, and having low concentrations of acrylic acid, e.g., not more than 10 parts per million, preferably not more than 8 parts per million, and more preferably not more than 5 parts per million, as described herein. Higher concentrations of acrylic acid may be detrimental for obtaining desirable butyl acrylate quality. Having lower concentrations of acrylic acid in the butyl acrylate stream can eliminate the need for further processing, e.g., the need to reduce acrylic acid by neutralization.
The processes of this invention further relate in part to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product comprising reacting at least one carboxylic acid-containing feedstock with at least one alcohol-containing feedstock in the presence of an esterification catalyst in a single reaction zone maintained under reaction conditions sufficient to produce at least one ester product, said reaction conditions comprising a temperature and pressure sufficient to crack heavies formed in or introduced into said single reaction zone and to vaporize at least a portion of said at least one ester product upon production thereof, and wherein said at least one carboxylic acid-containing feedstock comprises a crude acrylic acid stream containing acetic acid, acrylic acid dimer and/or other Michael-Addition heavies. In this embodiment, lower purity feed streams, for example, crude acrylic acid streams containing high concentrations, e.g., greater than about 0.25 weight percent or even greater than about 0.5 weight percent, of acrylic acid dimer and/or other Michael-Addition heavies may be utilized in the processes of this invention.
The processes of this invention find particular application in the production of esters, especially esters that contain ethylenic unsaturation or other reactive groups that can lead to unwanted side reactions. Advantageous processes include the formation of alkyl acrylates and alkyl methacrylates from lower alkanols, typically alcohols of one to twelve carbon atoms, and acrylic acid or methacrylic acid. A preferred aspect of this invention pertains to processes for making butyl acrylate from butanol and acrylic acid.